1. Technical Field
The aspects of the embodiments described herein relate to an apparatus and method for correcting flicker situations encountered in the use of dimmer units for lighting controls.
2. Background Art
Lighting controls are prevalent in both home and commercial applications. Some lighting controls are very simple, e.g., on/off switches, but others include remote operation and dimming controls, which can be manual or automatic. Regardless of how the dimming controls are operated, it is important that dimming controls operate properly. As those of skill in the art can appreciate, while conventional dimming technology has been available for a very long time, there are still some problems with existing technologies.
One such problem in dimming controls is referred to as “flicker.” Flicker is the condition in which the power or voltage that is transferred to the lamp is inconsistent over different cycles of 60 Hz or 50 Hz AC input voltage. This causes the lamp to become brighter and/or dimmer from cycle-to-cycle, ½ cycle to ½ cycle, or over multiple cycles, thereby exhibiting a flicker effect. While the human eye can average some discrepancies in different amounts of brightness over different cycles, due to, in part, its response time to light impulses, when the difference in amount of brightness due to changes in the control voltage reaches a certain threshold, the effect becomes significant. This can cause a reaction to those subjected to the flicker ranging from annoyance to headaches and other maladies. For example, photosensitive epilepsy (PSE) is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regularly moving patterns.
As known by those of skill in the art, dimming controls conventionally “throttle” or control the amount of voltage that is applied to the lamp (for purposes of this discussion, the “lamp” can be incandescent, fluorescent, or a light emitting diode (LED)). This throttling is based on time; i.e., a 50% reduction in brightness would translate to cutting off the voltage transferred to the lamp about half-way through each of the positive and negative half cycles. This typically would occur when the AC voltage reaches either its positive maximum or its negative maximum. The amount of energy delivered to the lamp is dependent upon the voltage-time product provided in the waveform or voltage applied to the lamp.
FIG. 1 illustrates a conventional wall mounted dimming control apparatus (dimmer) 100 for use in housing conventional dimming control circuitry 108 (which is discussed in greater detail in regard to FIG. 2). In FIG. 1, conventional house AC power (Hot_Power) 102 and neutral 104 are input to wall-mounted box 106, which houses dimming control circuitry 108. The output of wall-mounted box 106 is DIM_Hot output 110, which is connected to a first connector of lamp 112, and a second connector of lamp 112 is connected to neutral 104, which is also received and used by dimming control circuitry 108. DIM_Hot output 110 is a controlled version of Hot_Power 102 that dims lamp 112. Control of DIM_Hot output 110 occurs through action of switch 114, which, as those of skill in the art can appreciate, is generally a rotatable potentiometer that provides a variable voltage to additional circuitry (discussed in FIG. 2) that assists in generating DIM_Hot output 110.
FIG. 2 illustrates conventional dimming control circuitry 108 in greater detail. Dimming control circuitry 108 includes FET drive circuitry 210, which resides on DIM switch board 216, switch 114, first opto-isolator 212, and second opto-isolator 214. Dimming control circuitry 108 further includes a bi-directional switch that includes first and second MOSFETs (transistors Q1, Q2) 206, 208, which receives, as respective input drive signals, FET_A_DRV—1 input signal 202 and FET_B_DRV—1 input signal 204, which are generated by operation of switch 114, FET drive circuitry 210, and first and second opto-isolators 212, 214. FET drive circuitry 210 is a conventional FET drive generation circuit for the control of transistors Q1 and Q2 206, 208 known to those of skill in the art, and therefore a detailed explanation of such is not necessary in fulfillment of the dual purposes of clarity and brevity. FET_A_DRV—1 input signal 202 controls transistor Q1 206 through first opto-isolator 212, which isolates the high voltage transistor Q1 206 from certain portions of the circuitry on FET drive circuitry 210, and FET_B_DRV—1 input signal 204 controls transistor Q2 208 in a similar manner (i.e., isolation via second opto-isolator 214), both of which act together to control the flow of 120 VAC, or Hot_Power 102 in the form of DIM_Hot output 110 to lamp 112. FET_A_DRV—1 input signal 202 and FET_B_DRV—1 input signal 204 are generated by other circuitry which is not shown or discussed in fulfillment of the dual purposes of clarity and brevity. DIM switch board 216 can contain the circuitry that not only creates FET_A_DRV—1 input signal 202 and FET_B_DRV—1 input signal 204, but also switch 114, and other circuitry as well.
FET_A_DRV—1 input signal 202 and FET_B_DRV—1 input signal 204 control dimming of lamp 112 in the following manner. FET_A_DRV—1 input signal 202 controls transistor Q1 206 on for the positive and negative going portions of Hot_Power 102, and FET_B_DRV—1 controls Q2 208 on for the positive and negative portions of Hot_Power 102. When FET_A_DRV—1 input signal 202 is active, it turns on transistor Q1 206, allowing it to act as switch. Similarly, when FET_B_DRV—1 204 is active, it turns on Q2 208 allowing it to also act as a switch. For positive portions of Hot_Power 102, the positive current can flow through transistor Q1 206 from its drain to its source, and through Q2 208 from its source to drain, and then out of the Dim_Hot output 110. FET_A_DRV—1 input signal 202 and FET_B_DRV—1 input signal 204 will be active for some portion of the positive and negative voltage cycle of Hot_Power 102, to control the dimming of lamp 112. For negative portions of Hot_Power 102, the negative current flows into Dim_Hot 110, through transistor Q2 208 from its drain to source, and then through Q1 206 from its source to drain. Typically, FET_A_DRV—1 input signal 202 and FET_B_DRV—1 input signal 204 are symmetrical, and gated in time to cause the correct dimming of lamp 112 as known by those of skill in the art.
FIG. 3 illustrates normal dimming control power voltage signal DIM_Hot output 110 when there is no over- or under-shoot situation in the input 120 VAC power waveform (Hot_Power 102) and a flicker-causing dimming control power voltage signal when there is both an over- and under-shoot situation in DIM_Hot output 110. In a first example, Hot_Power 102, which is input to the bi-directional switch shown in FIGS. 1 and 2, is controlled such that only 50% brightness is desired, so that in conventional FET drive circuitry 210, only half of the positive and half of the negative going portions of Hot_Power 102 is allowed to conduct to lamp 112, and the resulting waveform is DIM_Hot output 110a. It can be readily appreciated that about half of each of the positive and negative portions of each 120 VAC cycle is now output to lamp 112. Decreasing the amount of energy that reaches lamp 112 reduces the brightness emitted therefrom. Because there is little or no variation in input Hot_Power 102 and thus output DIM_Hot output 110a, this results in a substantially if not completely non-flicker situation because Hot_Power 102 and DIM_Hot output 110 are substantially uniform and the energy sent to lamp 112 has been reduced proportional to the dimming control signal.
However, in the second example of DIM_Hot output 110b, there is an over-voltage condition, caused by an over-voltage in Hot_Power 102, shown as waveform peak 302. DIM_Hot overshoot 110b will reach the same overshoot level (302) above the normal peak voltage of Hot_Power 102, occurring at about halfway through the positive cycle of the AC power waveform. Consequently, the amount of energy sent to lamp 112 is greater than that which is normally sent. The energy that is transferred during each positive ½ cycle of DIM_Hot output 110a is represented by and shown as first volt-sec product 306; note that second volt-sec product 308 is larger than volt-sec product 306 due to the increase in amplitude of DIM_Hot output 110b at the portion that has been identified as over-volt condition 302, and thus an increase in brightness will result. In under-volt condition 304, which represents an under-voltage condition, third volt-sec product 310 is less than first volt-sec product 306, and a decrease in brightness will result. Both the increase in brightness and decrease in brightness cause flicker.
Another approach to dimming controls is shown in U.S. Pat. No. 7,259,524 to Hausman, et al (the '524 Patent). In the '524 Patent, an apparatus and methods for regulating delivery of electrical energy to a lighting load are described. An electrical waveform is received from a source of electrical energy. An integration value is then generated based on a square of an amplitude of the received waveform. Electrical energy is delivered to the load until the integration value exceeds a threshold value. Thereafter, the delivery of electrical energy to the load is discontinued. As can be appreciated by those of skill in the art, and as can be seen from the '524 Patent, Hausman describes a dimming control system that is fairly complicated—referring just to FIG. 1, it can be seen that there are many circuit devices and signal processing steps involved to control the load on the lamp. That is, a microcontroller, comparator, pulse waveform generator, sawtooth generator and other devices are needed to accomplish the dimming function. Furthermore, the number of amplifiers used to accomplish the dimming function as outlined in FIGS. 8A-8E is about a dozen, and further includes at least two integrated circuits. As those of skill in the art can appreciate, this type of cumbersome approach can lead to premature failure because of the significant number of active components used, as well as required additional power.
Accordingly, it would be desirable to provide methods, modes and systems for improving dimming control circuitry to reduce or substantially eliminate flicker situations.